1. Field of the Invention
The present invention relates to a diagnostic agent for diabetes and in particular to a diagnostic agent for diabetes which comprises glucose labelled with .sup.13 C at a specific position, or pyruvic acid labelled with .sup.13 C at least one specific position.
2. Description of the Prior Art
Test methods generally used in the primary screening in diagnosis of diabetes are urine sugar test and fasting blood sugar levels test. These tests are simple and high in specificity, but are low in sensitivity and give negative results for patients with light diabetes, so 70% or more patients are missed and these tests are considered inadequate as screening tests for diabetes (Sekikawa et al., Medical Practice 10:63, 1993). On the one hand, a glucose tolerance test used for the diagnosis of diabetes brings about side effects due to administration of a large amount of glucose, and this test requires the restraint of a subject for several hours and repeated collection of blood, and imposes heavy physical burdens on the subject, and further the procedures are troublesome, so this test is actually impossible to carry out as a screening test of diabetes. Recently, blood HbA1C and fructosamine tests, which reflect average of blood sugar levels for a certain period in the past, have been introduced as screening tests of diabetes in some facilities. Under the existing circumstances, however, even those tests are cannot be said to be adequate in sensitivity and specificity for light diabetes, and there remain the problem of a difference in measurement results among facilities.
Blood sugar level, HbA1C and fructosamine tests have been used widely for diagnosis of the type of diabetes, management of outpatients with diabetes, and evaluation of therapeutic effects. However, blood sugar levels would drop at the time of fasting in the case of light diabetes, while besides the above-described problems, the HbA1C and fructosamine tests have the problem that the results of the tests cannot be known until a next visit to the hospital, so instructions would be given to the patient on the basis of the past test results.
Under such circumstances, there is demand for developments in a test method which is effective for patients even with light diabetes and non-invasive to the subjects and which give results immediately and accurately for diagnosis of diabetes, management of patients with diabetes and evaluation of therapeutic effects.
On the one hand, it is generally carried out to administer .sup.13 C-labeled glucose and measure .sup.13 C exhausting as carbon dioxide into an exhalation in order to assess energy expenditure. Because this analysis should be conducted under steady state, glucose should be administered for a long period before examination [J. J. Robert et al., J. Appl. Physiol. 63, 1725-1732 (1987)]. Therefore, this analysis requires a long period for examination and imposes the heavy pains on the subject, and is thus practically not usable for diagnosis of diabetes.
It is reported that after naturally labelled .sup.13 C-glucose prepared from C.sub.4 plants is bolus administrated, the degree of exhalation of .sup.13 CO.sub.2 is reduced in the case of patients with diabetes [P. Lefebvre, et al., Diabetologia 14, 39-45 (1978); M. J. Arnaud, et al., Nutrition and the Diabetic Child, Pediat. Adolesc. Endocr. vol. 7, pp. 203-212, 1979]. However, because naturally labelled .sup.13 C-glucose have 6 carbons randomly labeled, we can scarecely evaluate an alternation of the metabolic pathway of glucose. Further, because the concentration of .sup.13 C in naturally labelled .sup.13 C-glucose is 2% or thereabout, it is necessary to administer a large amount of glucose in order to monitor a change in the concentration of CO.sub.2 in an exhalation, and the burdens on the subject are therefore heavy.